1. Field of the Invention
The present invention relates to a malfunction determination device for a motor control system that controls the operation of a motor.
2. Description of the Related Art
In recent years, motor control systems that include a state detection system that outputs a signal corresponding to the operation state of a motor to execute operation control of the motor based on an output signal of the state detection system are widely used.
Some conventional systems use a signal corresponding to the rotational phase of an output shaft of a motor which serves as an electric motor (for example, a pulse signal that varies periodically along with rotation of the motor output shaft) as the output signal of the state detection system. The rotational speed and the rotational phase of the output shaft of the motor may be determined by monitoring the output signal.
Japanese Patent Application Publication No. 2006-226226 (JP-A-2006-226226), for example, describes a system that uses a signal that indicates the rotational direction of an output shaft of a motor as the output signal. The system according to JP-A-2006-226226 outputs, as the signal that indicates the rotational direction of the motor output shaft, a Lo signal when the output shaft is rotating in the forward direction and a Hi signal when the output shaft is rotating in the reverse direction. The rotational direction of the motor output shaft (forward direction or reverse direction) may be determined by monitoring the output signal.
If a malfunction occurs in the motor control system, it is desirable to immediately determine that a malfunction has occurred and to change the operation control of the motor to a mode appropriate for such an occurrence. When a malfunction occurs in the motor control system (in a malfunction condition), the output signal of the state detection system often varies differently than when no malfunction occurs in the motor control system (in a normal condition). This makes it possible to determine that a malfunction has occurred in the motor control system based on the fact that the output signal varies differently from that at normal times.
However, in a system that only outputs either a Lo signal or a Hi signal in accordance with the rotational direction of the motor output shaft, the rotational direction of the motor output shaft indicated by the signal may match the actual rotational direction of the motor output shaft if a malfunction occurs that does not cause the Hi signal or Lo signal to vary from the rotational direction of the motor output shaft. At this time, even if a malfunction has occurred in the motor control system, the output signal of the state detection system happens to vary in the same manner as under normal operation. In this case, therefore, it is not possible to properly determine that a malfunction has occurred based only on the output signal of the state detection system.
Such inconveniences in detecting malfunctions discussed above occur not only in motor control systems that execute operation control of an electric motor but also in motor control systems that execute operation control of a linear motor with a reciprocally movable member, such as a plunger, for example.